The present invention relates to a fuel supply apparatus for an internal combustion engine, and more particularly, it relates to a fuel supply apparatus of the type in which a fuel injector operates to inject fuel toward a heater provided in an intake pipe of the engine.
FIG. 5 schematically shows the general arrangement of a known fuel supply apparatus for an internal combustion engine. In this figure, the illustrated internal combustion engine includes an engine proper 1 having a plurality of cylinders (only one is illustrated) and a corresponding number of pistons reciprocating therein. An intake pipe 2 is connected with the engine proper 1 for supplying an air/fuel mixture thereto. A control valve 3 is disposed in the intake pipe 2 for controlling the amount or flow rate of intake air supplied to the engine proper 1. A fuel injector 4 is disposed in the intake pipe 2 at a location upstream of the control valve 3 for injecting a proper or required amount of fuel into the intake pipe 2. A heater 5 is disposed in the intake pipe 2 at a location downstream of the control valve 3 for heating fuel, which is injected from the fuel injector 4 into the intake pipe 2, and for expediting evaporation thereof. The heater 5 in the form of an electric heating rod is fixedly attached at its opposite ends to the inner surface of the intake pipe 2 through a pair of holders or brackets 6.
In operation, the fuel injector 4 is controlled by an unillustrated control means to inject a proper amount of fuel into the intake pipe 2 in accordance with the opening degree of the control valve 3 which is determined by an operating condition of the engine. The injected fuel is mixed with intake air in the intake pipe 2 and sucked together into the engine proper 1 via the intake pipe 2, while being heated by the heater 5 to expedite evaporation thereof. The thus evaporated air/fuel mixture is supplied into respective cylinders of the engine proper 1 and combusted therein. In this manner, fuel evaporation due to the heater 5 serves to atomize the injected fuel into finer particles to increase combustion efficiency in comparison with the use of a general type of fuel injector without any heater which is disposed near an intake valve provided in an intake port in each cylinder head for controlling fuel supply to a corresponding cylinder.
However, the above-mentioned known fuel supply apparatus involves the following disadvantages. In the known fuel supply apparatus, the heater 5 is disposed in a perpendicular relation with respect to air streams in the intake pipe 2 so that it somewhat presents an obstacle to the air streams, thus causing a pressure loss of the intake air. This may result in adverse effects during intake strokes of the engine.
Japanese Patent Laid-Open No. 58-48773 discloses another example in which a heater is disposed on and near the wall of an intake pipe. In this prior art, too, a fuel injector injects fuel toward the heater, so during a high load engine operation, for example, in which a relatively great amount of fuel is injected from the injector, the injected fuel is heated to be atomized by the heater before introduction into respective engine cylinders. As a consequence, a lot of energy is consumed by the heater for heating and atomizing such a great amount of fuel, resulting in an impairment or reduction in fuel economy.